Pulmonary fibrosis is a serious medical problem affecting more than 200,000 patients in the U.S. At present, there are few treatments available to counteract pulmonary fibrosis. Modulation of the renln-anglotensin system has been suggested, but the efficacy of such strategies remains uncertain and somewhat contradictory. My project is to evaluate whether other substrates of ACE beside angiotensin II may play a significant role. My approach was to develop two new strains of mice by homologous recombination in order to mutate the specific amino acids responsible for zinc binding (and thus catalysis) in each domain of ACE. In mice termed N-KO, the N-termlnal domain of ACE is Inactivated. In C-KO mice, It is the C-terminal domain that is no longer catalytic. The cardiovascular and renal phenotypes of N-KO and C-KO mice are indistinguishable from wild-type mice. These mouse models are ideal to study specific functions of ACE independent of blood pressure changes, a typical bias In studying the RAS with pharmacologic manipulations. I have now shown that the tetrapeptide AcSDKP, a specific substrate of the N-terminal catalytic site of ACE protects mice from bleomycin-induced lung Injury. The next step of my investigation is to analyze the molecular mechanisms responsible for AcSDKP protection. My hypothesis is that it is mediated by an inhibition ofthe TFG-beta/Smad pathway. This will be evaluated by determining the phosphorylation of Smad proteins and their translocation to the nucleus. The last part of my project consists of determining if these observations in N-KO mice could be transposed to other animal models. I will investigate if administration of AcSDKP to wild-type mice protects them from bleomycin-induced lung injury. Preliminary observations suggest that AcSDKP administration alone limits the inflammation without preventing the development of fibrosis. This may be due to the high expression of ACE in the lung and the rapid degradation of AcSDKP in that organ. I will therefore test the co-administration of AcSDKP and ACE inhibitors.